tion. An especially striking difference between crude and intrinsic birth rates appears in the 1959-61 figures, when the projection would lead to an increase from the observed 22.74 to 24.30 in 1970 and to 27.31 ultimately. This increase is due to the action of the age-specific birth and death rates in replenishing the very small generation of women bom in the 1930's. The advance 1969 birth figures show a rise in the crude rate without much change from the previous year in age-specific rates, owing to an age distribution more favorable to fertility.
Fortunately for many applications, departures of the observed from the stable age distribution in developing countries are smaller than in the United States.
Various Intrinsic Rates of Natural Increase
The intrinsic rate we have been calculating here answers the question: How fast would the population ultimately increase if its age-specific rates of birth and death continued for a long time? The importance of such an intrinsic rate does not depend on the age-specific rates in fact continuing into the future; it tells us what they mean now. Nonetheless the stress on the intrinsic rate as contrasted with the crude rates is justified by the thought that age-specific fertility is more likely to be a continuing characteristic of women than their overall fertility with the (possibly peculiar) age distribution that they happen to have at the present moment.
But other elements than age surely exist—what about marriage? If the proportion of the population married at the moment happens to be higher than the proportion that would be married with the continuance of the current age-specific marriage rates, then it would seem that overall fertility would be higher now than it would be in the long run. The identical argument used to justify the treatment of age in the age-intrinsic rate justifies the corresponding treatment of marriage.
To see the meaning of various possible directions of adjustment for the United States in 1960, consider the following five rates computed by Frank Oechsli (7):
Crude Crude rate of natural increase 14.7 per 1,000
A Age-intrinsic rate 20.8
A-N Age-nuptiality intrinsic rate 18.4
A-P Age-parity intrinsic rate 23.0
A-N-P Age-nuptiality-parity intrinsic rate 19.6
The rise when we go from the crude rate in the first line to the age-intrinsic rate in the second means that the observed age distribution was unfavorable to increase—that there was a smaller proportion of women ofe in the present than in the past.